Families accrue advantages through their investments in their immediate members and in their relationships with kin and a variety of personal associates. Although the term investment is quite familiar to relationship and family scholars (e.g., Goodfriend and Agnew, 2008; Rusbult, Drigotas, and Verette, 1994), in recent decades it has been given new focus through the idea of social capital, a concept that has found a captive audience principally among network scholars and sociologists. Despite the controversies that have arisen concerning this construct (Lin, 2001a; Portes, 1998; Sandefur and Laumann, 1998), we believe that its value warrants further attempts to clarify the essential meaning of the concept. In particular, we believe that family and relationship scholarship is especially well suited both to guide this clarification and to benefit from integrating this concept into its work. In this chapter, we present an understanding of how this integration might unfold.